Methods for formulating a cement slurry for use in a subterranean salt formation using geometric modeling

ABSTRACT

Methods including experimentally determining a salt creep profile for a single salt or intercalated salts in a subterranean formation, designing a proposed cement slurry based on the salt creep profile, experimentally determining whether the proposed cement slurry is capable of forming a wellbore load resistant cement sheath based on actual thermal and thermo-mechanical properties of the proposed cement slurry, theoretically determining whether the proposed cement slurry is capable of forming the wellbore load resistant cement sheath by designing an electronic, cross-section geometric model of the subterranean salt formation and simulating a condition of the wellbore loads on the cured proposed cement slurry using the geometric model, establishing a final cement slurry capable of forming the wellbore load resistant cement sheath, and performing a final cementing operation with the final cement slurry in the subterranean salt formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of PCT/US2014/040245 entitled“Methods for Formulating a Cement Slurry for Use in a Subterranean SaltFormation,” filed May 30, 2014.

BACKGROUND

The embodiments herein relate to methods for formulating a cement slurryfor use in a subterranean salt formation, and, more particularly, tomethods for formulating a cement slurry in a subterranean salt formationcomprising single and intercalated salts using geometric modeling.

Subterranean formation operations (e.g., stimulation operations, sandcontrol operations, completion operations, etc.) often involve drillinga wellbore in a subterranean formation with a drilling fluid (andthereafter placing a cement sheath between the formation and a casing(or liner string) in the wellbore. The cement sheath is formed bypumping a cement slurry through the bottom of the casing and out throughan annulus between the outer casing wall and the formation face of thewellbore, or by directly pumping a cement slurry into the annulus. Thecement slurry then cures in the annular space, thereby forming a sheathof hardened cement that, inter alia, supports and positions the casingin the wellbore and bonds the exterior surface of the casing to thesubterranean formation. This process is referred to as “primarycementing.” Among other things, the cement sheath may keep fresh waterreservoirs from becoming contaminated with produced fluids from withinthe wellbore. As used herein, the term “fluid” refers to liquid phasefluids and gas phase fluids. The cement sheath may also prevent unstableformations from caving in, thereby reducing the chance of a casingcollapse and/or stuck drill pipe. Finally, the cement sheath forms asolid barrier to prevent fluid loss or contamination of productionzones. The degree of success of a subterranean formation operationinvolving placement of a cement sheath, therefore, depends, at least inpart, upon the successful cementing of the wellbore casing and thecement's ability to maintain zonal isolation of the wellbore.

Formations below the subterranean salt formations are often rich inhydrocarbons or other desirable fluids for production to the surface.Thus, drilling and cementing wellbores in such subterranean saltformations is often performed to reach such zones and produce thehydrocarbons to the surface. As used herein, the term “subterranean saltformation” (or simply “salt formation”) refers to a rock formationcomposed substantially of salt. A variety of salts may be found in asalt formation including, but not limited to, halite, sylvite,bischofite, carnallite, polyhalite, tachyhydrite, anhydrite, and thelike, and any combination thereof. However, drilling and cementing insuch salt formations may be problematic due to salt creep, for example.As used herein, the term “salt creep” refers to the phenomenon of saltin a formation under stress to deform significantly as a function oftime, depending on the loading conditions, and its physical properties,which permits the salt to flow into the wellbore and replace the volumeof formation removed by the drill bit. Such replacement may reduce thesize of the wellbore and/or may cause the drill pipe to stick andeventually force abandonment of the well. Additionally, during drilling,a drilling fluid may be circulated to and from a wellbore and salt fromthe formation may become dissolved in the drilling fluid, resulting in,among other things, wellbore opening (i.e., an increase in theradius/diameter of the wellbore), changes in the rheology of thedrilling fluid, and the like.

During cementing, the cement slurry may interact with and dissolve atleast a portion of the salts in the salt formation, thereby affectingthe hydration properties and final cured properties of a cement slurry.For example, dissolution of salt in the cement slurry may influence suchcement properties as, without limitation, free fluid, thickening time,compressive strength, rheological properties, and the like. In somecases, the influence of the salt dissolution by changing the geometry ofthe wellbore and the cement slurry properties may be particularlydetrimental and may result in the failure of zonal isolation in awellbore (e.g., by reducing the wellbore radius and through fluidinvasion or other loss of structural integrity to the hydrating or curedcement). Failure of zonal isolation, among other things, may result inenvironmental contamination, which may cause harm to both flora andfauna, including humans. Such failure may further prevent production orreduce the production capability of a wellbore, which may result inabandonment of the wellbore or costly and time-consuming remedialactions.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of theembodiments, and should not be viewed as exclusive embodiments. Thesubject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, as willoccur to those skilled in the art and having the benefit of thisdisclosure.

FIG. 1 illustrates a representation of an electronic, cross-sectiongeometric model at a location comprising a single salt, according to oneor more embodiments of the present disclosure.

FIG. 2 illustrates a representation of an electronic, cross-sectiongeometric model simulating the plane-strain condition of a single saltat a location in a wellbore in a subterranean salt formation, accordingto one or more embodiments of the present disclosure.

FIG. 3 illustrates a representation of an electronic, longitudinalgeometric model at a length comprising intercalated salts, according toone or more embodiments of the present disclosure.

FIG. 4 illustrates a representation of an electronic, longitudinalgeometric model simulating the axisymmetric condition of intercalatedsalts at a first length in a wellbore in a subterranean salt formation,according to one or more embodiments of the present disclosure.

FIG. 5 illustrates a graph depicting the remaining capacity for arepresentative proposed cured cement slurry subjected to wellbore loadsin the presence of a formation and casing, according to one or moreembodiments of the present disclosure.

FIG. 6 illustrates an embodiment of a system configured for deliveringthe final cement slurries described herein to a downhole location,according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

The embodiments herein relate to methods for formulating a cement slurryfor use in a subterranean salt formation, and, more particularly, tomethods for formulating a cement slurry in a subterranean salt formationcomprising single and intercalated salts using geometric modeling.

The methods described in the embodiments of the present disclosurepermit an operator to determine whether a particular cement slurryformulation may be used in a particular subterranean salt formation toform a cement sheath. Generally, the methods of the present disclosureoptimize cement sheath mechanical properties for cementing single andintercalated salt zones in a wellbore in a subterranean salt formationusing customized geometric modeling and analysis of the wellboreconstruction process, such that the optimized cement sheath is capableof maintaining mechanical integrity for the life of the wellbore underplanned wellbore loadings, including salt creep loads of the one or moresalts adjacent to the cement sheath.

The methods described herein may take into account specific salt creepprofiles, wellbore loads (e.g., natural loads, operational loads, saltcreep loads, and the like), and the like. More specifically, the methodsdescribed herein may take into account the presence of a single salt orintercalated salt layers. As used herein, the term “intercalated salt”refers to at least two salt layers, which may abut one another orcomprise one or more layers of a geological formation materialtherebetween or adjacent thereto (e.g., mineral or rock layers).Accordingly, the methods described herein take into account the varyingwellbore loads that may be present at a location or along a length of awellbore where a single salt, intercalated salt layers, and/or anygeological material layers therebetween or flanking such single orintercalated salt layers, in which each exerts different wellbore loadpressures on a hydrating or cured cement sheath. As used herein, theterm “hydrating” or “hydration” refers to the process of a cementreaction with water as it proceeds to its cured state, but before finalcuring. As used herein, the term “cure” or “cured” refers to cement thathas set, hardened, and completed substantially its reaction with water.

Accordingly, and as discussed in detail below, based on the results of asalt creep profile and various wellbore loads, the methods of thepresent disclosure utilize an electronic geometric model to simulate theintegrity of the cement sheath to withstand such loads. The geometricmodel beneficially may take into account a single salt (e.g., a singlesalt layer) or intercalated salts, including any intercalated geologicalformation materials, to simulate the effect of the wellbore loads atvarious locations at a location or along a length of a wellbore due todiffering physical wellbore loads and differing physical locations. Thecement slurry may be manipulated one or more times and re-evaluated toensure that it is appropriate for the particular subterranean saltformation and any subterranean formation operations to be performedtherein (e.g., drilling, stimulation, production, and the like). Once anadequate cement slurry has been designed for use in the subterraneansalt formation, a cementing operation may be performed with knowledgethat the cement slurry will provide long-term zonal isolation.

One or more illustrative embodiments disclosed herein are presentedbelow. Not all features of an actual implementation are described orshown in this application for the sake of clarity. It is understood thatin the development of an actual embodiment incorporating the embodimentsdisclosed herein, numerous implementation-specific decisions must bemade to achieve the developer's goals, such as compliance withsystem-related, lithology-related, business-related, government-related,and other constraints, which vary by implementation and from time totime. While a developer's efforts might be complex and time-consuming,such efforts would be, nevertheless, a routine undertaking for those ofordinary skill in the art having benefit of this disclosure.

It should be noted that when “about” is provided herein at the beginningof a numerical list, the term modifies each number of the numericallist. In some numerical listings of ranges, some lower limits listed maybe greater than some upper limits listed. One skilled in the art willrecognize that the selected subset will require the selection of anupper limit in excess of the selected lower limit. Unless otherwiseindicated, all numbers expressing quantities of ingredients, amounts oftime, and so forth used in the present specification and associatedclaims are to be understood as being modified in all instances by theterm “about.” As used herein, the term “about” encompasses +/−5% of anumerical value. Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by the exemplary embodimentsdescribed herein. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claim,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

While compositions and methods are described herein in terms of“comprising” various components or steps, the compositions and methodscan also “consist essentially of” or “consist of” the various componentsand steps. When “comprising” is used in a claim, it is open-ended.

As used herein, the term “substantially” means largely, but notnecessarily wholly.

The methods described in the present disclosure generally employ a fourstep methodology, which is not presented sequentially as the sequencemay vary, involving (1) characterizing the subterranean salt formationinto which a cement sheath is to be placed, (2) designing a cementslurry and testing for its thermal and thermo-mechanical properties, (3)modeling a well construction process by constructing a geometricwellbore model and representing wellbore loads expected to be exerted onthe wellbore mathematically (and in sequence) taking into account theformation, cured cement sheath, and casing, and (4) performing astructural analysis of the casing-cement-formation (i.e., taking intoaccount each component in a wellbore including the formation, thecasing, and the cement for a particular cementing operation) todetermine the structural and mechanical integrity of the cement sheath.

In some embodiments, the methods described herein include providing awellbore in a subterranean salt formation comprising a single salt at afirst location in the salt formation. That is, in some embodiments, onlya single salt at a particular location in the salt formation may beanalyzed for forming a suitable cement sheath in accordance with theembodiments described herein. In other embodiments, the methodsdescribed herein include providing a wellbore in a subterranean saltformation comprising intercalated salts at a first length in the saltformation. That is, in some embodiments, multiple salt layers spanning aparticular length of the wellbore may be analyzed for forming a suitablecement sheath in accordance with the embodiments described herein, withor without geological material therebetween or abutting suchintercalated salts.

A salt creep profile for either the single salt at the first location orthe intercalated salt at the first length of the subterranean formationmay then be experimentally determined. As used herein, the term “saltcreep profile” refers to the salt creep loads placed on an adjacentstructure from salt in a subterranean formation. In the embodimentsherein, the structure adjacent to the salt in the formation may behydrating and cured cement for use in forming a cement sheath, and myfurther be casing adjacent to the cement sheath. The salt creep profilemay be determined by any method that quantifies the salt creep load.

In some embodiments, the salt creep profile may be experimentallydetermined by obtaining one or more wellbore core samples of thewellbore in the subterranean salt formation (e.g., at at least the firstlocation for the single salt, or at at least the first length for theintercalated salts). Without limitation, multiple wellbore core samplesmay be taken at varying locations or lengths along the wellbore, withoutdeparting from the scope of the present disclosure. Moreover, thewellbore core sample may comprise not only the single salt orintercalated salts of interest, but also geological formation material(e.g., geological formation material between or abutting the single orintercalated salts), without departing from the scope of the presentdisclosure. Thereafter, a core sample salt creep load measurement may beperformed to acquire the salt creep profiled.

In other embodiments, the salt creep profile may be experimentallydetermined by taking a downhole salt creep load measurement within thewellbore in the subterranean salt formation (i.e., without taking aphysical core sample, but within the physical wellbore) at one or morewellbore locations or lengths (e.g., at at least the first location forthe single salt, or at at least the first length for the intercalatedsalts). For example, the downhole salt creep load measurement mayevaluate wellbore radius closure rates due to salt creep with drillingmud or another treatment fluid within the wellbore. Such downhole saltcreep load measurements may be taken by any suitable downhole toolincluding, but not limited to, wellbore logs, such as caliper logs, andthe like that can measure wellbore size.

In yet other embodiments, the salt creep profile of the subterraneansalt formation of interest at one or more locations or lengths thereof(e.g., at at least the first location for the single salt, or at atleast the first length for the intercalated salts) may be experimentallydetermined by obtaining an offset well salt creep load measurement,without taking either a physical sample or a physical measurement of thesubterranean salt formation. As used herein, the term “offset well”refers to an existing wellbore close in proximity to a proposed wellthat provides information for planning the proposed well. In someembodiments, the offset well is in the same oil field as thesubterranean salt formation of interest. As used herein, the term “oilfield” refers to the surface area above a subsurface oil accumulation.Thereafter, parametric analysis may be performed on the offset well saltcreep load measurement to obtain the salt creep profile for thesubterranean salt formation of interest. Parametric analysis may beperformed to adjust for certain uncertainties and variability betweenthe offset well and the salt formation of interest. These uncertaintiesmay exist in the form of differences in salt creep profiles betweensalts of an offset well and the subterranean salt formation of interestdue to differences in moisture content, temperature, stresses, and thelike. In such cases, parametric analysis may be performed to understandthe effect of changing salt creep profile on cement sheath mechanicalintegrity of a proposed cement slurry.

Combinations of the various methods of experimentally determining thesalt creep profile of the subterranean salt formation at the one or morelocations or lengths of the wellbore thereof may also be employed,without departing from the scope of the present disclosure. Suchcombinations may, in some instances, enhance the accuracy of the saltcreep profile by averaging the various data, taking into account certainerror factors that may be present in the various methods, if at all,and/or statistically evaluating the various data, and the like.

Regardless of the method of obtaining the salt creep load measurement(e.g., the core sample salt creep load measurement, the downhole saltcreep load measurement, the offset salt creep load measurement, and thelike), the salt creep load measurement may be determined by anyvalidated strain rate-stress relationship that can represent saltbehavior in the subterranean salt formation. Salts are ductile and havea tendency to undergo deformation in the presence of non-hydrostaticstress states. When salt creep occurs in the absence of cement andcasing, the result is partial or complete closure of a wellbore.However, when a cement sheath is present in an annulus between thewellbore and casing, the cement sheath (and the casing) is subject tosalt creep load. That is, in-situ salt formations may be at non-creepingequilibrium state as their stress state is isotropic; however,subterranean formation operations (e.g., drilling, cementing,stimulation, and the like) disturb this equilibrium and salt creepresults. Moreover, even if the salt formation was in a creeping state,such subterranean formation operations may influence the creepingbehavior.

Salt creep may be divided into three distinct states: primary,secondary, and tertiary. Primary salt creep (also known as transientsalt creep) is characterized by high deformation in a short period oftime. As a salt is subjected to constant loading, the rate ofdeformation increases at a decreasing rate until it reaches a steadystate of deformation, known as secondary salt creep. Secondary saltcreep is the longest stage with respect to time and is where strain ratetends to become constant. Finally, tertiary salt creep is characterizedat the point in which the rate of deformation increases exponentiallyuntil failure of salt is reached. Accordingly, tertiary salt creepcauses a volume increase due to fracturing (e.g., microfracturing) inthe formation and leads to material failure.

The salt creep load measurements performed for determining the saltcreep profiles of the methods of the present disclosure may take intoaccount only secondary salt creep, which is the most dominant andlengthy stage for preparation of a final cement slurry according to theembodiments herein. In other embodiments, however, tertiary salt creepmay also be considered during the salt creep analyses described herein,particularly to evaluate different temperatures and stress loading. Inyet other embodiments, primary salt creep may be used in the salt creepanalyses; however, primary salt creep tends to be quite short lived andmay have very little, if any, effect on the salt creep profile.Accordingly, the salt creep load measurements for determining the saltcreep profile may take into account secondary salt creep only, secondaryand tertiary salt creep only, or all three stages of salt creep, withoutdeparting from the scope of the present disclosure.

As discussed above, the salt creep load measurement for primary,secondary, and tertiary salt creep in forming the salt creep profiles ofthe present disclosure may be determined by any validated strainrate-stress relationship that can represent salt behavior in asubterranean salt formation. In some embodiments, for example, secondarysalt creep can be determined using the following model:

$\begin{matrix}{{\overset{.}{ɛ}}_{2} = {{A_{1}{\exp\left( \frac{- Q_{1}}{RT} \right)}\left( \frac{S_{2}}{S_{2}^{o}} \right)^{n_{1}}} + {A_{2}{\exp\left( \frac{- Q_{2}}{RT} \right)}\left( \frac{S_{2}}{S_{2}^{o}} \right)^{n_{2}}}}} & {{Model}\mspace{14mu} 1}\end{matrix}$

where {dot over (ε)}₂ is the second invariant of deviatoric strain; S₂is the second invariant of deviatoric creep strain; Q₁ is the activationenergy for the first creep mechanism; Q₂ is the activation energy forthe second creep mechanism; and A₁, A₂, n₁, n₂, and S₂ ^(o) are materialconstants for the particular salt type in the formation. The materialconstants are determined using uniaxial and triaxial creep tests onextracted wellbore core samples. One of skill in the art will understandthe tests to be performed, as no single standard procedure is available.As such, the material constants may be determined by one of skill in theart and the outcome generally depends greatly on the procedure followedduring testing. Accordingly, it may be best to report results of uni-and triaxial creep tests along with testing protocol. The stress andstrain invariants are mathematically connected to individual stressesand strains, such relationships being available in any standardmechanical engineering textbook and known to those of skill in the art.While Model 1 is one of the salt creep models available, as known tothose of skill in the art, for example, there are other models that maybe used in the methods of the present disclosure. For example, some saltcreep models are based on microscopic deformation mechanisms, whileothers are purely empirical or combinations thereof. The methodsdisclosed herein are not limited to use of the salt creep analysisdefined by Model 1, but any existing or new models defining creepingphenomenon may be used, as the model itself does not affect the methodfollowed, but merely changes the model equation used.

There is no standard equation(s) for tertiary salt creep because it is afailure phenomenon; however, one of skill in the art will understand howto calculate such tertiary salt creep, if it is desired to be used inthe methods described herein, based on such factors as the failing salttype, the amount of failing salt, and the like.

Where intercalated salts are evaluated in a subterranean salt formationaccording to the methods described herein at one or more lengths, thesalt creep profile should take into account the salt creep load for eachsalt type. Moreover, where geological material is layered between orabutting the salt layers (or a single salt), the wellbore loads of suchlayers may also be desirably taken into account, depending on theparticular analysis being performed, as such layers will have differentwellbore load stresses exerted on a cement sheath.

A proposed cement slurry may then be designed based on theexperimentally determined salt creep profile. The proposed cement slurryis designed based on the salt creep profile for use in a proposedcementing operation involving forming a wellbore load resistant cementsheath within an annulus between the subterranean formation and casingin the formation. The “wellbore load resistant cement sheath,” as usedherein refers to a cured cement formulation that is resistant, orcapable of withstanding, wellbore loads of the subterranean saltformation at one or more locations or lengths thereof (e.g., at at leastthe first location for the single salt, or at at least the first lengthfor the intercalated salts). As used herein, the term “wellbore loads”refers to pressure, stress, weight, or any other load exerted on astructure in a wellbore (e.g., a cement sheath, casing, and the like).Such wellbore loads may be exerted from the subterranean formation(e.g., salt creep loads), exerted from a structure in the wellboreitself (e.g., casing), exerted from a subterranean formation operationbeing performed (e.g., drilling, cementing, production, and the like),and the like.

Examples of wellbore loads may include, but are not limited to, the saltcreep load previously discussed, a pressure load, a shut-in load, aproduction load, an injection load, a casing load, and any combinationthereof. As used herein, the term “pressure load” refers to stressesexperienced when exerting a surface pressure by hydraulic or mechanicalmeans, either inside the casing or in the annulus. The term “shut-inload,” as used herein, refers to stresses experienced when the wellboreis closed at the top (i.e., at the surface). The term “production load,”as used herein, refers to stresses experienced when hydrocarbons arebeing produced in the subterranean formation. As used herein, the term“injection load refers to stresses experienced when a hot fluid or acold fluid is being injected into the wellbore through casing or tubing.As used herein, the term “casing load” (also referred to as “linerload”) refers to axial stresses exerted by casing or liner weight.

The proposed cement slurry designed based on the salt creep profileexhibits a rheological profile based on the rheology of the proposedcement slurry. As used herein, “rheology” refers to the flow of matter,particularly in the liquid or semi-liquid state. The rheological profilemay be used to manipulate the proposed cement slurry, as discussedbelow, to establish a final cement slurry that is capable of forming thewellbore load resistant cement sheath described herein. Any rheologyparameter may be used to establish the rheological profile of theproposed cement slurry and may depend on a number of factors including,but not limited to, the specific type and composition of the proposedcement slurry, the type and composition of the subterranean saltcomposition, including single salt and/or intercalated salts, and thelike. Examples of rheology parameters that may establish the rheologicalprofile of the proposed cement slurry may include, but are not limitedto, plastic viscosity, Bingham model yield point, Herschel-Bulkley modelparameters, and any combination thereof.

The proposed cement slurry based on the salt creep profile to form awellbore load resistant cement sheath resistant to wellbore loads (whichinclude salt creep loads) may comprise a number of different components.Generally, any component suitable for use in forming a cement andcapable of use in a subterranean formation, which may form a wellboreload resistant cement sheath according to the embodiments describedherein, may be suitable for use in the methods of the presentdisclosure. Examples of suitable components for use in designing theproposed cement slurry are described in detail below.

After designing a proposed cement slurry, the proposed cement slurry isevaluated to experimentally determine and theoretically determinewhether it is capable of forming the wellbore resistant cement sheath atone or more locations or lengths (e.g., at at least the first locationfor the single salt, or at at least the first length for theintercalated salts). That is, the experimental and theoreticaldeterminations are based on the salt creep profile and wellbore loadsfor which data has been gathered at the one or more wellbore locationsor lengths.

Experimental determination of whether the proposed cement slurry iscapable of forming the wellbore resistant cement sheath may be performedby curing the proposed cement slurry and experimentally determining theactual thermal and thermo-mechanical properties thereof. Theseproperties are then used in structural analysis to determine if thecement sheath stresses are lower than the failure properties of thecement sheath. Such structural analysis includes formation of thegeometric model described herein, which may be formed using the actualthermal and thermo-mechanical properties or theoretical thermal andthermo-mechanical properties, as described in detail below. Experimentaldetermination of whether the proposed cement slurry is capable offorming the wellbore resistant cement slurry may be performed by firstcuring the proposed cement slurry and performing one or more tests todetermine the actual thermal and thermo-mechanical properties thereof.Such experimental determination may be performed by subjecting the curedproposed cement slurry to wellbore load conditions expected within thesubterranean formation during actual cementing operations. However, insome embodiments, such wellbore load conditions may not be feasiblyachievable in a non-subterranean formation setting (e.g., underlaboratory conditions), in which the maximum loading feasible may beused instead (termed herein “maximum laboratory load conditions”). Anylessening in the amount of loading compared to the actual wellbore loadsmay be compensated for using the theoretical determination comprisingforming a geometric model, as described in detail below. Moreover, insome instances, loadings greater than the expected wellbore loads may beused during the experimental determination to ensure that unexpected orunknown loadings are also taken into account (termed herein “excesswellbore load conditions”), without departing from the scope of thepresent disclosure.

In some embodiments, experimental determination may be performed byfirst curing the proposed cement slurry, followed by performing anultrasonic cement analyzer test on the cured proposed cement slurry.Ultrasonic cement analyzer testing may utilize a non-destructive methodfor determining the relative strength development of the cured proposedcement slurry under wellbore load conditions, maximum laboratory loadconditions, or excess wellbore load conditions, which may be based, forexample, on ultrasonic pulse velocity in the cured proposed cementslurry and its compressive strength. As previously discussed, the curedproposed cement slurry may be subjected to loads greater than thewellbore loads, without departing from the scope of the presentdisclosure. Such may be desirable in finally establishing the finalcement slurry capable of forming the wellbore load resistant cementsheath, as described below, to account for any unknown or unexpectedwellbore loads that the wellbore load resistant cement sheath mayencounter.

In other embodiments, experimental determination of whether the proposedcement slurry is capable of forming the wellbore resistant cement sheathmay be performed by first curing the proposed cement slurry andperforming uniaxial and triaxial compression tests on the cured proposedcement slurry under wellbore load conditions, maximum laboratory loadconditions, or excess wellbore load conditions. The results from suchexperimental determination are then used in structural analysis todetermine if the cement sheath stresses are lower than the failureproperties of the cement sheath. Such uniaxial and triaxial compressiontests may be destructive in nature and performed using any known orunknown techniques and methodology, as the methodology itself does notaffect the method of the present disclosure followed, but merely changesthe testing methodology equation used. The uniaxial and triaxialcompression tests test the capacity of the cured proposed cement slurryto withstand wellbore loads that tend to reduce size (e.g., crush orcompact, and the like) in one or three directions, respectively. Again,the cured proposed cement may be subjected to loads greater than thewellbore loads, without departing from the scope of the presentdisclosure.

The actual thermal and thermo-mechanical properties are determined bycuring the proposed cement slurry and performing a battery of testsusing the methods described above. Such tests may include, but are notlimited to, uniaxial experiments, triaxial experiments, tensile strengthtesting, thermal conductivity and specific heat and thermal expansiontesting, and shrinkage testing. Such testing may be performed accordingto the American Society for Testing and Materials procedures D3148-02,D2664-95a, C307, C470/C470M, C1608, or American Petroleum InstituteRecommended Practice 10B-2, or other standard testing methodologies.

Combinations of the various methods of experimentally determiningwhether the proposed cement slurry is capable of forming a wellbore loadresistant cement sheath at the one or more locations or lengths of thewellbore thereof may also be employed, without departing from the scopeof the present disclosure. Such combinations may, in some instances,enhance the accuracy of the experimental determination by averaging thevarious data, taking into account certain error factors that may bepresent in the various methods, if at all, and/or statisticallyevaluating the various data, and the like.

Theoretically determining whether the proposed cement slurry is capableof forming the wellbore load resistant cement sheath at one or morelocations or lengths in the wellbore of the subterranean salt formation(e.g., at at least the first location for the single salt, or at atleast the first length for the intercalated salts) may be determined byfirst designing an electronic geometric model of the subterranean saltformation at the one or more locations or lengths. Each operationalphase of a wellbore (e.g., drilling, running casing, cementing,wait-on-cement, pressure testing, production, and the like) may resultin new temperature and fluid pressures within casing in the wellbore.Numerically, these are represented in the form of temperature andpressure changes inside the casing. Due to the changing values, thecasing-cement-formation structural response may be modeled, andquantified as stresses. Of particular importance to the presentdisclosure are the stresses in the cement sheath (e.g., the curedproposed cement slurry, and the cured final cement slurry, discussedbelow), which may be dependent upon the operational phase beingperformed, temperatures, and pressures—equating to the wellbore loadsdescribed herein—applied inside the casing or from the subterraneanformation. In some embodiments, the structural response of thecasing-cement-formation may be quantified numerically using a finiteelement technique or any other numerical solution technique oranalytical/semi-analytical technique capable of solving stress-strainrelationships for solid structures.

Where a single salt is located at a first location in a wellbore in asubterranean salt formation, the electronic geometric model may be anelectronic, cross-section geometric model representing the subterraneansalt formation, the casing, and the proposed cement slurry after curingat the first location. Although described herein as modeling a singlelocation having a single salt, at least a second location in thesubterranean salt formation comprising another salt (which may be of thesame or different type) may also be analyzed and have an electronicgeometric model prepared according to the description herein, withoutdeparting from the scope of the present disclosure. The electronic,cross-section geometric model is thus a two-dimensional cross-section ofthe wellbore in the subterranean salt formation at the first location ofinterest comprising the single salt. Referring now to FIG. 1,illustrated is a representation of an electronic, cross-sectiongeometric model at a location comprising a single salt. As depicted,three concentric circular structures are shown, depicting from the innermost concentric structure to the outermost: the casing, cement, andsubterranean formation. FIG. 1 is an illustrative example, and the sizeand shape of the casing, cement, and formation will not berepresentative of all wellbores. FIG. 1 is for illustrative purposesonly and in no way is meant to limit the present disclosure.

The first location comprising the single salt in the subterraneanformation may be representative of the area in which the single saltexhibits the greatest salt creep load, so as to take into account themost severe loading in establishing a final cement slurry capable offorming the wellbore load resistant cement sheath, as described below.Such salt creep loads, along with the remaining wellbore loads ofinterest, are tested using the electronic, cross-section geometric modelby simulating a plane-strain condition of such wellbore loads on thecured proposed cement slurry at the first location (or additionallocations). As used herein, the term “plane-strain” refers to thedeformation of a structure (e.g., the cured proposed cement slurry, thecasing, and the like) in which the deformation is parallel to a givenplane. For the wellbore load exertion on the subterranean salt formationat a location comprising a single salt, where such exertion istheoretically determined using an electronic, cross-section geometricmodel, the wellbore loads are radially compressive in nature and,accordingly, compression may be the only failure mechanism resultingfrom the wellbore loads.

The plane-strain condition of the wellbore loads simulated using theelectronic, cross-section geometric model of the present disclosure atthe first location (or any other locations) for a single salt may besimulated based on the wellbore loads and one or both of: (1) thetheoretical thermal and thermo-mechanical properties of the curedproposed cement slurry, or (2) the actual thermal and thermo-mechanicalproperties of the cured proposed cement slurry established during theexperimental determination of whether the proposed cement slurry iscapable of forming the wellbore load resistant cement slurry describedherein. For example, the experimental determination of whether theproposed cement slurry is capable of forming the wellbore load resistantcement slurry may be first performed to acquire the actual thermal andthermo-mechanical properties before simulating the plane-straincondition (or axisymmetric condition, or three-dimensional condition, asdiscussed below) of the wellbore loads. In other embodiments, thetheoretical determination may be first performed by simulating theplane-strain condition (or axisymmetric condition, or three-dimensionalcondition, as discussed below) with the theoretical thermal andthermo-mechanical properties, followed by the experimentaldetermination. In yet other embodiments, either or both of theexperimental determination and theoretical determination may beperformed in any order and repeated several times. For example, thetheoretical determination may be first performed, followed by theexperimental determination, followed again by the theoreticaldetermination using the actual thermal and thermo-mechanical properties,without departing from the scope of the present disclosure. In someembodiments, the plane-strain condition of the wellbore loads simulatedusing the electronic, cross-section geometric model may also take intoaccount the elastic and failure properties of the casing and thesubterranean salt formation, which may be obtained based on known typesof casing and subterranean salt formations to one of skill in the art.

The thermal and thermo-mechanical properties of the cured proposedcement slurry used to theoretically determine whether the cured proposedcement slurry is capable of forming the wellbore load resistant cementsheath based may be calculated based on one or more of thermalconductivity, thermal diffusivity, tensile strength, compressivestrength, hydration volume change, Young's modulus, and Poisson's ratio.

The theoretical thermal and thermo-mechanical properties of the curedproposed cement slurry may be based on scientifically availablehistorical data related to such properties of similar cement slurriesthat have been used in the past and tested, including those used insimilar subterranean salt formations (e.g., offset wells). Thetheoretical thermal and thermo-mechanical properties based on historicaldata are compared against the wellbore loads that are expected to beexerted on the cured proposed cement slurry.

The actual thermal and thermo-mechanical properties are determined bycuring the proposed cement slurry and performing a battery of tests asdescribed above with reference to the experimental determination ofwhether the proposed cement slurry is capable of forming the wellboreload resistant cement sheath of the present disclosure.

Referring now to FIG. 2, illustrated is an electronic, cross-sectiongeometric model simulating the plane-strain condition of a single saltat a first location in a wellbore in a subterranean salt formation.Shown is a representative cured proposed cement slurry forming a cementsheath accounting for wellbore loads exerted thereupon, and taking intoaccount the thermal and thermo-mechanical properties of the curedproposed cement slurry (i.e., actual and/or theoretical). As shown, theradial stresses exerted on the external, outermost portion of the curedproposed cement slurry (i.e., the portion in contact with thesubterranean salt formation (not shown)) exhibit stresses of about 23.07megapascals (MPa), and up to the next range of radial stress of about26.93 MPa. Moving toward the casing (not shown), these radial stressesincrease as increased pressure is placed on the cured proposed cementsheath, up to as high as about 30.86 MPa for the innermost portion ofthe cured proposed cement slurry, for the representative cured proposedcement slurry shown. If the radial stresses shown in the plane-strainsimulation of the electronic, cross-section geometric model exceed theability of the cured proposed cement slurry to resist such wellboreloads, the cured proposed cement slurry will fail by compression.Moreover, by representing the radial stresses shown in FIG. 2, forexample, as a fraction of the compressive strength of the proposedcement slurry, the proximity of the proposed cement slurry to failuremay also be defined. The “proximity” is a stress-state factor, where astress-state factor close to failure has a high risk of failure andvice-versa. FIG. 2 is an illustrative example and the radial stressesexhibited will not be representative of all cured cement slurries andmay vary in any numerical direction depending at least upon the wellborestresses encountered. FIG. 2 is for illustrative purposes only and in noway is meant to limit the present disclosure.

Referring now to the methods described herein related to intercalatedsalts, where intercalated salts are located at a first length in awellbore in a subterranean salt formation for use in the embodimentsdescribed herein, the electronic geometric model may be an electronic,longitudinal geometric model representing the subterranean saltformation, the casing, and the proposed cement slurry after curing alongthe first length. The electronic, longitudinal geometric model may betwo-dimensional, three-dimensional, or may possess characteristics ofboth two-dimensions and three-dimensions, without departing from thescope of the present disclosure. Although described herein as modeling asingle length having intercalated salts (e.g., at least two salt layersabutting one another or between or adjacent to geological material), atleast a second length (e.g., one or more additional lengths, or theentire length) in the subterranean salt formation comprising otherintercalated salts (which may be of the same or different type) may alsobe analyzed and have an electronic geometric model prepared according tothe description here, without departing from the scope of the presentdisclosure. The electronic, longitudinal geometric model is thus alength-wise model of the wellbore in the subterranean salt formation atthe first length of interest comprising the intercalated salts, and mayrepresent the subterranean salt formation, the casing, and the proposedcement slurry after curing.

Referring now to FIG. 3, illustrated is a representative electronic,longitudinal geometric model that may be designed in accordance with themethods of the present disclosure having represented thereonintercalated salts. As depicted, the electronic, longitudinal geometricmodel depicts a length-wise representation of a subterranean saltformation comprising two different salts and an area of overburden andsub-salt. The overburden and sub-salt areas are located at the top-mostand bottom-most length, respectively, of the electronic, longitudinalgeometric model of the wellbore, each having matching visual texturerepresentations (diagonal parallel lines at about 45° from an upperright to a lower left). The overburden and sub-salt areas representnon-creeping portions of the wellbore and may, in some instances,represent non-creeping salt material or other geological material, asdescribed above. Such overburden and sub-salt areas may be taken intoaccount in analyzing wellbore loads and establishing a final cementslurry capable of forming a wellbore load resistant cement slurry. Thetwo textures between the overburden and sub-salt areas represent theintercalated layering of two salts, halite and tachyhydrite, the firsttexture beneath the overburden (diagonal parallel lines from an upperright to a lower left) being halite and the second texture beneath theoverburden (diagonal parallel lines from an upper left to a lower right)being tachyhydrite. FIG. 3 is an illustrative example and types,amounts, and positions of the intercalated salts exhibited will not berepresentative of all subterranean salt formations or portions thereof.FIG. 3 is for illustrative purposes only and in no way is meant to limitthe present disclosure. Moreover, although FIG. 3 represents a verticalwellbore, deviated and horizontal wellbores may also be representedusing the methods described herein, without departing from the scope ofthe present disclosure.

Typically, each of the various intercalated salts will have differentsalt creep load rates (e.g., some slower than others, some faster thanothers, and the like); additionally, and any geological material willlikely also exhibit different loading rates. Such salt creep loads,along with the remaining wellbore loads of interest, are tested usingthe electronic, longitudinal geometric model by simulating anaxisymmetric condition or three-dimensional condition of such wellboreloads on the cured proposed cement slurry at the first length (oradditional lengths). As used herein, the term “axisymmetric condition”refers to the deformation of a structure (e.g., the cured proposedcement slurry, the casing, and the like) about a symmetrical axis,including in two- and three-dimensions. As used herein, the term“three-dimensional condition” refers to the deformation of a structure(e.g., the cured proposed cement slurry, the casing, and the like)irrespective of an axis relationship (e.g., in lengths of a subterraneanformation that are not axisymmetric). For the wellbore load exertion onthe subterranean salt formation at a length comprising intercalatedsalts, where such exertion is theoretically determined using anelectronic, longitudinal geometric model, the wellbore loads are thusradially compressive and tensile in nature and vary at differentlocations along the length of the wellbore.

The axisymmetric condition or three-dimensional condition of thewellbore loads simulated using the electronic, longitudinal geometricmodel of the present disclosure at the first length (or any otherlengths) for intercalated salts may be simulated based on the wellboreloads and one or both of: (1) the theoretical thermal andthermo-mechanical properties of the cured proposed cement slurry, or (2)the actual thermal and thermo-mechanical properties of the curedproposed cement slurry established during the experimental determinationof whether the proposed cement slurry is capable of forming the wellboreload resistant cement slurry described herein. The theoretical andactual thermal and thermo-mechanical properties may be obtained asdescribed previously with reference to the plane-strain condition of theelectronic, cross-section geometric model for single salts in asubterranean salt formation and the experimental determination ofwhether the proposed cement slurry is capable of forming the wellboreload resistant cement slurry described herein. In some embodiments, theaxisymmetric condition or three-dimensional condition of the wellboreloads simulated using the electronic, longitudinal geometric model mayalso take into account the elastic and failure properties of the casingand the subterranean salt formation, which may be obtained based onknown types of casing and subterranean salt formations to one of skillin the art.

Referring now to FIG. 4, illustrated is an electronic, longitudinalgeometric model simulating the axisymmetric condition of intercalatedsalts at a first length in a wellbore in a subterranean salt formation.As shown, the length of the wellbore has exerted thereupon differingwellbore loads at different locations along the length of the wellbore.Specifically, the wellbore is shown as exhibiting varying salt creeploads that impinge into the wellbore causing wellbore closure in theabsence of casing and cement, but rather in the presence of only atreatment fluid (e.g., drilling mud). As shown, the wellbore is closingat different rates and amounts due to different salt creep rates of thevarious intercalated salts, depicted as protrusions to the left of thewellbore. The longer the protrusion, the greater the salt creep rate. Ifthe cured proposed cement slurry were positioned adjacent to thewellbore represented in FIG. 4, certain portions of the cured proposedcement slurry would be more compressed relative to other portions alongthe length represented. Further, at junctions between slow and fastcreeping salts, the cured proposed cement slurry would be pushedradially inward on the fast creeping salt side and pushed radiallyoutward on the slow creeping salt side, resulting in a tensile load onthe proposed cured cement. Accordingly, for the cured proposed cementslurry to fail as a cement sheath, either the tensile stresses exceedthe cement tensile strength, or the compressive stresses exceed thecement compressive strength. Often, the tensile strength of the cementis much reduced compared to the compressive strength and, thus, may becritical in manipulating the proposed cement slurry to establish a finalcement slurry capable of forming a wellbore load resistant cementsheath. FIG. 4 is an illustrative example and the salt creep loads andrates will vary among differing subterranean salt formations. FIG. 4 isfor illustrative purposes only and in no way is meant to limit thepresent disclosure.

As previously mentioned, the sequence of experimental determination andtheoretical determination of whether the proposed cement slurry iscapable of forming the wellbore resistant cement slurry is not limitingand they may be performed in any order, without departing from the scopeof the present disclosure. Determining experimentally whether theproposed cement slurry, once cured into a cement sheath, can actuallywithstand the wellbore loads and form a wellbore load resistant cementsheath may be particularly laborious and may thus be preferablyperformed only after theoretically determining that the proposed cementslurry is likely to withstand such loads, thereby reducing thelikelihood of having to repeat the step, although repeating the stepdoes not depart from the scope of the present disclosure. For example,one or more experimental determinations may be performed before one ormore theoretical determinations, and in some instances the actualthermal and thermo-mechanical properties may then be used in performingthe theoretical determination by simulating the wellbore load conditionsusing the geometric model. In other embodiments, one or more theoreticaldeterminations may be performed before one or more experimentaldeterminations.

If at any point during the experimental determination or the theoreticaldetermination of whether the proposed cement slurry is capable offorming the wellbore resistant cement slurry for a particularsubterranean salt formation (e.g., comprising a single salt orintercalated salts, as well as other geological material), thecomposition of the proposed cement slurry may be manipulated and newproposed cement slurry may be evaluated using the experimental and/ortheoretical determination of whether the newly formed proposed cementslurry is capable of forming the wellbore resistant cement slurry. Uponoptimizing the proposed (one or more iterations) clement slurry based onthe methods of the present disclosure such that it is capable of formingthe wellbore resistant cement slurry, it may be termed a “final cementslurry”, which may be used during an actual cementing operation in theparticular subterranean salt formation of interest.

Manipulation of the proposed cement slurry, for example, may beperformed after performing the one or more experimental determinationsof whether the proposed cement slurry is capable of forming the wellboreload resistant cement sheath, but before performing the one or moretheoretical determinations of whether the proposed cement slurry iscapable of forming the wellbore load resistant cement sheath, followedby repeating one, or both, of the one or more experimentaldeterminations and the one or more theoretical determinations in anyorder until a final cement slurry is established that is capable offorming the wellbore load resistant cement sheath and performing a finalcementing operation with the final cement slurry. In other embodiments,manipulation of the proposed cement slurry, for example, may beperformed after performing the one or more theoretical determinations ofwhether the proposed cement slurry is capable of forming the wellboreload resistant cement sheath, but before performing the one or moreexperimental determinations of whether the proposed cement slurry iscapable of forming the wellbore load resistant cement sheath, followedby repeating one, or both, of the one or more theoretical determinationsand the one or more experimental determinations in any order until afinal cement slurry is established that is capable of forming thewellbore load resistant cement sheath and performing a final cementingoperation with the final cement slurry.

In yet other embodiments, manipulation of the proposed cement slurry,for example, may be performed after performing both of the one or moreexperimental determinations and the one or more theoreticaldeterminations of whether the proposed cement slurry is capable offorming the wellbore load resistant cement sheath, followed by repeatingone, or both, of the one or more experimental determinations and the oneor more theoretical determinations in any order until a final cementslurry is established that is capable of forming the wellbore loadresistant cement sheath and performing a final cementing operation withthe final cement slurry.

In some embodiments, the proposed cement slurry, alone or aftermanipulation, may meet the requirements of a final cement slurry capableof forming the wellbore load resistant cement sheath for a particularsubterranean salt formation and for particular subterranean operationsbeing performed therein. However, an operator may further choose tomanipulate the proposed cement slurry to account for potential stressesthat may be further imposed on the cured proposed cement slurry forminga cement sheath. That is, if for the selected operational phase theproposed cement slurry is capable of forming a wellbore load resistantcement sheath, it qualifies as a final cement slurry. However, theproposed cement slurry may be even further manipulated to form anoptimized final cement slurry that takes into account remainingcapacity. As used herein, the term “remaining capacity” is a scaledvalue, representing the maximum acceptable value of compressive and/ortensile wellbore loads (stresses) scaled to the ultimate compressive ortensile strength of the proposed cement slurry. If the resultantremaining capacity is below an operator defined recommended value, whichmay account for potential unknown or unexpected wellbore loads, theproposed cement slurry may be further manipulated in accordance with anyof the methods described above (e.g., before or after one or both of theexperimental and/or theoretical determination of whether the proposedcement slurry is capable of forming the wellbore load resistant cementsheath) by further accounting for the remaining capacity in addition tothe wellbore loads.

Referring now to FIG. 5, illustrated is a graph depicting the remainingcapacity for a representative proposed cured cement slurry subjected towellbore loads in the presence of a formation and casing. The remainingcapacities depicted in FIG. 5 are in compressive (also referred to asshear) and tensile mode for a representative electronic, longitudinalgeometric model (not shown) of a length in a wellbore in a subterraneansalt formation comprising intercalated salts. As shown, the remainingcapacity of each of the various intercalated salt types is an indicationof the remaining capacity (i.e., the residual elastic capacity) in thecured proposed cement slurry before failure. A 100% remaining capacityindicates that the cured proposed cement slurry subjected to wellboreloads is completely intact, while a 0% remaining capacity indicates thatfailure of the cured proposed cement slurry.

In some embodiments, the designed proposed cement slurry and establishedfinal cement slurry (collectively referred to below as “cement slurry”unless specifically stated otherwise) may comprise an aqueous base fluidand a cementitious material. Any aqueous base fluid suitable for use informing a curable cement slurry capable of use in a subterranean saltformation may be suitable for use in the embodiments described herein.In particular, the suitable aqueous base fluids for use in the proposedand final cement slurries discussed herein may be any aqueous base fluidsuitable for use in the subterranean formation, as previously discussed,including, but not limited to, freshwater, saltwater, brine, seawater,and any combination thereof. Generally, the aqueous base fluid may befrom any source provided, for example, that it does not contain anexcess of compounds that may undesirably affect the performance of theproposed or final cement slurry or the pumpability thereof. For example,the aqueous base fluid may be recovered from a subterranean formation,recycled from a treatment fluid previously used, treated wastewater, andthe like, without departing from the scope of the present disclosure.

The cementitious material of the embodiments herein may be anycementitious material suitable for use in forming a curable cementslurry. In preferred embodiments, the cementitious material may be ahydraulic cement. Hydraulic cements harden by the process of hydrationdue to chemical reactions to produce insoluble hydrates (e.g., calciumhydroxide) that occur independent of the cement's water content (e.g.,hydraulic cements can harden even under constantly damp conditions).Thus, hydraulic cements are preferred because they are capable ofhardening regardless of the water content of a particular subterraneanformation. Suitable hydraulic cements may include, but are not limitedto Portland cement, Portland cement blends (e.g., Portland blast-furnaceslag cement and/or expansive cement), non-Portland hydraulic cement(e.g., super-sulfated cement, calcium aluminate cement, and/or highmagnesium-content cement), and any combination thereof. Generally, thecementitious material may be present in the cement slurries describedherein to achieve a cement slurry density in the range of from a lowerlimit of about 9.0 pounds per gallon (“ppg”), 10 ppg, 11 ppg, 12 ppg, 13ppg, 14 ppg, 15 ppg, 16 ppg, and 17 ppg to an upper limit of about 25ppg, 24 ppg, 23 ppg, 22 ppg, 21 ppg, 20 ppg, 19 ppg, 18 ppg, and 17 ppg,encompassing any value and subset therebetween.

In some embodiments, the cement slurry may additionally comprise apozzolanic material. Pozzolanic materials may aid in increasing thedensity and strength of the cementitious material. As used herein, theterm “pozzolanic material” refers to a siliceous material that, whilenot being cementitious, is capable of reacting with calcium hydroxide(which may be produced during hydration of the cementitious material).Because calcium hydroxide accounts for a sizable portion of mosthydrated hydraulic cements and because calcium hydroxide does notcontribute to the cement's properties, the combination of cementitiousand pozzolanic materials may synergistically enhance the strength andquality of the cement. Any pozzolanic material that is reactive with thecementitious material may be used in the embodiments herein. Suitablepozzolanic materials may include, but are not limited to silica fume,metakaolin, fly ash, diatomaceous earth, calcined or uncalcineddiatomite, calcined fullers earth, pozzolanic clays, calcined oruncalcined volcanic ash, bagasse ash, pumice, pumicite, rice hull ash,natural and synthetic zeolites, slag, vitreous calcium aluminosilicate,and any combinations thereof. In some embodiments, the pozzolanicmaterial may be present in an amount in the range of a lower limit ofabout 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, and32.5% to an upper limit of about 60%, 57.5%, 55%, 52.5%, 50%, 47.5%,45%, 42.5%, 40%, 37.5%, 35%, and 32.5% by weight of the dry cementitiousmaterial, encompassing any value and subset therebetween.

In some embodiments, the cement slurry may further comprise any cementadditive for use in forming a curable cement slurry. Cement additivesmay be added in order to modify the characteristics of the cementslurry, for example. Such cement additives include, but are not limitedto, a defoamer, a cement accelerator, a cement retarder, a fluid-lossadditive, a cement dispersant, a cement extender, a weighting agent, alost circulation additive, and any combination thereof. The cementadditives of the embodiments herein may be in any form, including dryform or liquid form.

Manipulation of the proposed cement slurry in accordance with themethods of the present disclosure as provided above, therefore, mayinvolve altering one or more of the amount, type, presence, or absenceof one or more components of the slurry (e.g., the aqueous base fluid,the cementitious material, the pozzolanic material, the cement additive,and any combination thereof). That is, in some embodiments, the type ofbase fluid may be changed or adjusted (e.g., adding fresh water toseawater). In other embodiments, a pozzolanic material may be added whenit was not present before, the type of cementitious material may becompletely changed or a new blend proposed, a cement additive may beremoved or added from the proposed cement slurry, and the like. Thecombinations of changes are not limited and one of skill in the art,with the benefit of this disclosure, will understand how those changeswill affect the proposed cement slurry, with an eye toward manipulatingthe proposed cement slurry such that it is capable of forming thewellbore load resistant cement sheath described herein.

In various embodiments, systems configured for preparing, transporting,and delivering the final cement slurries described herein to a downholelocation are described. In various embodiments, the systems can comprisea pump fluidly coupled to a tubular (e.g., a casing, drill pipe,production tubing, coiled tubing, etc.) extending into a wellborepenetrating a subterranean formation, the tubular may be configured tocirculate or otherwise convey a final cement slurry prepared asdescribed herein. The pump may be, for example, a high pressure pump ora low pressure pump, which may depend on, inter alia, the viscosity anddensity of the final cement slurry, the type of the cementing operation,and the like.

In some embodiments, the systems described herein may further comprise amixing tank arranged upstream of the pump and in which the final cementslurry is formulated. In various embodiments, the pump (e.g., a lowpressure pump, a high pressure pump, or a combination thereof) mayconvey the final cement slurry from the mixing tank or other source ofthe final cement slurry to the tubular. In other embodiments, however,the final cement slurry can be formulated offsite and transported to aworksite, in which case the final cement slurry may be introduced to thetubular via the pump directly from a transport vehicle or a shippingcontainer (e.g., a truck, a railcar, a barge, or the like) or from atransport pipeline. In yet other embodiments, the final cement slurrymay be formulated on the fly at the well site where components of thefinal cement slurry are pumped from a transport (e.g., a vehicle orpipeline) and mixed during introduction into the tubular. In any case,the final cement slurry may be drawn into the pump, elevated to anappropriate pressure, and then introduced into the tubular for deliverydownhole.

FIG. 6 shows an illustrative schematic of a system that can deliverfinal cement slurry of the present disclosure to a downhole location,according to one or more embodiments. It should be noted that while FIG.6 generally depicts a land-based system, it is to be recognized thatlike systems may be operated in subsea locations as well. As depicted inFIG. 6, system 1 may include mixing tank 10, in which a final cementslurry of the present disclosure may be formulated. Again, in someembodiments, the mixing tank 10 may represent or otherwise be replacedwith a transport vehicle or shipping container configured to deliver orotherwise convey the final cement slurry to the well site. The finalcement slurry may be conveyed via line 12 to wellhead 14, where thefinal cement slurry enters tubular 16 (e.g., a casing, drill pipe,production tubing, coiled tubing, etc.), tubular 16 extending fromwellhead 14 into wellbore 22 penetrating subterranean formation 18. Uponbeing ejected from tubular 16, the final cement slurry may subsequentlyreturn up the wellbore in the annulus between the tubular 16 and thewellbore 22 as indicated by flow lines 24. In other embodiments, thefinal cement slurry may be reverse pumped down through the annulus andup tubular 16 back to the surface, without departing from the scope ofthe disclosure. Pump 20 may be configured to raise the pressure of thefinal cement slurry to a desired degree before its introduction intotubular 16 (or annulus). It is to be recognized that system 1 is merelyexemplary in nature and various additional components may be presentthat have not necessarily been depicted in FIG. 6 in the interest ofclarity. Non-limiting additional components that may be present include,but are not limited to, supply hoppers, valves, condensers, adapters,joints, gauges, sensors, compressors, pressure controllers, pressuresensors, flow rate controllers, flow rate sensors, temperature sensors,and the like. Moreover, reverse cementing, where the final cement slurryis directly placed in the annulus between the tubular 16 and thewellbore 22 may also be performed in accordance with the embodimentsdescribed herein, without departing from the present disclosure.

One skilled in the art, with the benefit of this disclosure, shouldrecognize the changes to the system described in FIG. 6 to provide forother cementing operations (e.g., squeeze operations, reverse cementing(where the cement is introduced into an annulus between a tubular andthe wellbore and returns to the wellhead through the tubular), and thelike).

It is also to be recognized that the disclosed final cement slurries mayalso directly or indirectly affect the various downhole equipment andtools that may come into contact with the final cement slurry duringoperation. Such equipment and tools may include, but are not limited to,wellbore casing, wellbore liner, completion string, insert strings,drill string, coiled tubing, slickline, wireline, drill pipe, drillcollars, mud motors, downhole motors and/or pumps, surface-mountedmotors and/or pumps, centralizers, turbolizers, scratchers, floats(e.g., shoes, collars, valves, etc.), wellbore projectiles (e.g.,wipers, plugs, darts, balls, etc.), logging tools and related telemetryequipment, actuators (e.g., electromechanical devices, hydromechanicaldevices, etc.), sliding sleeves, production sleeves, plugs, screens,filters, flow control devices (e.g., inflow control devices, autonomousinflow control devices, outflow control devices, etc.), couplings (e.g.,electro-hydraulic wet connect, dry connect, inductive coupler, etc.),control lines (e.g., electrical, fiber optic, hydraulic, etc.),surveillance lines, drill bits and reamers, sensors or distributedsensors, downhole heat exchangers, valves and corresponding actuationdevices, tool seals, packers, cement plugs, bridge plugs, and otherwellbore isolation devices, or components, and the like. Any of thesecomponents may be included in the systems generally described above anddepicted in FIG. 6.

Embodiments disclosed herein include Embodiment A and Embodiment B.

Embodiment A

A method comprising: (a) providing a wellbore in a subterranean saltformation, wherein the subterranean salt formation comprises a singlesalt at a first location; (b) experimentally determining a salt creepprofile for the single salt at the first location in the wellbore in thesubterranean formation; (c) designing a proposed cement slurry based onthe salt creep profile, the proposed cement slurry having a rheologyprofile, wherein the proposed cement slurry is designed for use in aproposed cementing operation involving forming a wellbore load resistantcement sheath within an annulus between the subterranean salt formationand casing, and wherein the wellbore load resistant cement sheath isresistant to wellbore loads; (d) experimentally determining whether theproposed cement slurry is capable of forming the wellbore load resistantcement sheath at the first location based on actual thermal andthermo-mechanical properties of the proposed cement slurry; (e)theoretically determining whether the proposed cement slurry is capableof forming the wellbore load resistant cement sheath at the firstlocation, the theoretical determination comprising: (e)(1) designing anelectronic, cross-section geometric model of the subterranean saltformation at the first location, wherein the geometric model representsthe subterranean salt formation, the casing, and the proposed cementslurry after curing, and (e)(2) simulating a plane-strain condition ofthe wellbore loads on the cured proposed cement slurry at the firstlocation in the subterranean formation using the geometric model, (f)establishing a final cement slurry capable of forming the wellbore loadresistant cement sheath; and (g) performing a final cementing operationwith the final cement slurry in the subterranean salt formation.

Embodiment A may have one or more of the following additional elementsin any combination:

Element A1: Wherein the salt creep profile in step (b) is experimentallydetermined by a method selected from the group consisting of: (b1)obtaining at least one wellbore core sample of the wellbore in thesubterranean formation at the first location, and performing a coresample salt creep load measurement using the wellbore core sample, (b2)performing a downhole salt creep load measurement at the first locationin the wellbore in the subterranean formation; (b3) obtaining an offsetwell salt creep load measurement and performing a parametric analysisthereon, wherein the offset well and the wellbore in the subterraneansalt formation are located in a same oil field, and any combinationthereof.

Element A2: Wherein the wellbore loads are selected from the groupconsisting of a salt creep load, a pressure load, a shut-in load, aproduction load, an injection load, and any combination thereof.

Element A3: Wherein whether the proposed cement slurry is capable offorming the wellbore load resistant cement sheath in step (d) isexperimentally determined by a method selected from the group consistingof: (d1) curing the proposed cement slurry, and performing an ultrasoniccement analyzer test on the cured proposed cement slurry, (d2) curingthe proposed cement slurry, and performing uniaxial and triaxialcompression tests on the cured proposed cement slurry, and anycombination thereof.

Element A4: Wherein the plane-strain condition of the wellbore loads onthe cured proposed cement slurry at the first location in thesubterranean formation using the geometric model in step (e)(2) issimulated based the wellbore loads and one or both of: theoreticalthermal and thermo-mechanical properties of the cured proposed cementslurry, or the actual thermal and thermo-mechanical properties of thecured proposed cement slurry in step (d).

Element A5: Wherein the plane-strain condition of the wellbore loads onthe cured proposed cement slurry at the first location in thesubterranean formation using the geometric model in step (e)(2) issimulated based the wellbore loads and one or both of: theoreticalthermal and thermo-mechanical properties of the cured proposed cementslurry, or the actual thermal and thermo-mechanical properties of thecured proposed cement slurry in step (d); and wherein step (e) isperformed before step (d), wherein step (e)(2) is simulated based on thetheoretical thermal and thermo-mechanical properties, and furthercomprising repeating a second step (e) after step (d) wherein the secondstep (e) comprises step (e)(2) of simulation based on the actualtheoretical thermal and thermo-mechanical properties in step (d).

Element A6: Further comprising either performing step (d) before step(e), or performing step (e) before step (d).

Element A7: Further comprising manipulating the proposed cement slurryafter step (d), and repeating steps (d) through (e) until the proposedcement slurry is capable of forming the wellbore load resistant cementsheath.

Element A8: Further comprising manipulating the proposed cement slurryafter step (e), and repeating steps (d) through (e) until the proposedcement slurry is capable of forming the wellbore load resistant cementsheath.

Element A9: Wherein the salt creep profile is based on secondary saltcreep; a combination of secondary salt creep and tertiary salt creep; ora combination of primary salt creep, secondary salt creep, and tertiarysalt creep.

Element A10: Further comprising a tubular extending into the wellbore inthe subterranean salt formation, and a pump fluidly coupled to thetubular; and wherein step (g) is performed by introducing the finalcement slurry into the wellbore through the tubular.

By way of non-limiting example, exemplary combinations applicable toEmbodiment A include: A with A1 and A4; A with A2, A6, and A10; A withA2, A3, A5, and A9; A with A7 and A8; A with A1, A2, A3, A4, A5, A6, A7,A8, A9, and A10; A with A4, A7, A8, and A10; and the like.

Embodiment B

A method comprising: (a) providing a wellbore in a subterranean saltformation, wherein the subterranean salt formation comprisesintercalated salts along a first length of the wellbore; (b)experimentally determining a salt creep profile for the intercalatedsalts at the first length of the wellbore in the subterranean formation;(c) designing a proposed cement slurry based on the salt creep profile,the proposed cement slurry having a rheology profile, wherein theproposed cement slurry is designed for use in a proposed cementingoperation involving forming a wellbore load resistant cement sheathwithin an annulus between the subterranean salt formation and casing,and wherein the wellbore load resistant cement sheath is resistant towellbore loads; (d) experimentally determining whether the proposedcement slurry is capable of forming the wellbore load resistant cementsheath at the first length based on actual thermal and thermo-mechanicalproperties of the proposed cement slurry; (e) theoretically determiningwhether the proposed cement slurry is capable of forming the wellboreload resistant cement sheath at the first length, the theoreticaldetermination comprising: (e)(1) designing an electronic, longitudinalgeometric model of the subterranean salt formation at the first length,wherein the geometric model represents the subterranean salt formation,the casing, and the proposed cement slurry after curing, and (e)(2)simulating an axisymmetric condition or a three-dimensional condition ofthe wellbore loads on the cured proposed cement slurry at the firstlocation in the subterranean formation using the geometric model, (f)establishing a final cement slurry capable of forming the wellbore loadresistant cement sheath; and (g) performing a final cementing operationwith the final cement slurry in the subterranean salt formation.

Embodiment B may have one or more of the following additional elementsin any combination:

Element B1: Wherein whether the proposed cement slurry is capable offorming the wellbore load resistant cement sheath in step (d) isexperimentally determined by a method selected from the group consistingof: (d1) curing the proposed cement slurry, and performing an ultrasoniccement analyzer test on the cured proposed cement slurry, (d2) curingthe proposed cement slurry, and performing uniaxial and triaxialcompression tests on the cured proposed cement slurry, and anycombination thereof.

Element B2: Wherein the wellbore loads are selected from the groupconsisting of a salt creep load, a pressure load, a shut-in load, aproduction load, an injection load, and any combination thereof.

Element B3: Wherein the axisymmetric condition or the three-dimensionalcondition of the wellbore loads on the cured proposed cement slurry atthe first length in the subterranean formation using the geometric modelin step (e)(2) is simulated based the wellbore loads and one or both of:theoretical thermal and thermo-mechanical properties of the curedproposed cement slurry, or the actual thermal and thermo-mechanicalproperties of the cured proposed cement slurry in step (d).

Element B4: Wherein the axisymmetric condition or the three-dimensionalcondition of the wellbore loads on the cured proposed cement slurry atthe first length in the subterranean formation using the geometric modelin step (e)(2) is simulated based the wellbore loads and one or both of:theoretical thermal and thermo-mechanical properties of the curedproposed cement slurry, or the actual thermal and thermo-mechanicalproperties of the cured proposed cement slurry in step (d); and whereinstep (e) is performed before step (d), wherein step (e)(2) is simulatedbased on the theoretical thermal and thermo-mechanical properties, andfurther comprising repeating a second step (e) after step (d) whereinthe second step (e) comprises step (e)(2) of simulation based on theactual theoretical thermal and thermo-mechanical properties in step (d).

Element B5: Wherein the electronic, longitudinal geometric model is athree-dimensional model.

Element B6: Further comprising either performing step (d) before step(e), or performing step (e) before step (d).

Element B7: Further comprising manipulating the proposed cement slurryafter step (d), and repeating steps (d) through (e) until the proposedcement slurry is capable of forming the wellbore load resistant cementsheath.

Element B8: Further comprising manipulating the proposed cement slurryafter step (e), and repeating steps (d) through (e) until the proposedcement slurry is capable of forming the wellbore load resistant cementsheath.

Element B9: Further comprising repeating steps (b) through (e) at atleast a second length of the wellbore in subterranean salt formation,wherein the electronic, longitudinal geometric model designed in step(e)(1) represents the first length and at least the second length.

Element B10: Wherein the salt creep profile is based on secondary saltcreep; a combination of secondary salt creep and tertiary salt creep; ora combination of primary salt creep, secondary salt creep, and tertiarysalt creep.

Element B11: Further comprising a tubular extending into the wellbore inthe subterranean salt formation, and a pump fluidly coupled to thetubular; and wherein step (g) is performed by introducing the finalcement slurry into the wellbore through the tubular.

By way of non-limiting example, exemplary combinations applicable toEmbodiment B include: B with B1, B2, and B11; B with B3, B5, B7, and B9;B with B1 and B4; B with B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, andB11; B with B5, B9, and B10; B with B1, B4, B6, and B11; and the like.

Therefore, the embodiments disclosed herein are well adapted to attainthe ends and advantages mentioned as well as those that are inherenttherein. The particular embodiments disclosed above are illustrativeonly, as they may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularillustrative embodiments disclosed above may be altered, combined, ormodified and all such variations are considered within the scope andspirit of the present disclosure. The embodiments illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces.

The invention claimed is:
 1. A method comprising: (a) providing awellbore in a subterranean salt formation, wherein the subterranean saltformation comprises a single salt at a first location; (b)experimentally determining a salt creep profile for the single salt atthe first location in the wellbore in the subterranean formation; (c)designing a proposed cement slurry based on the salt creep profile, theproposed cement slurry having a rheology profile, wherein the proposedcement slurry is designed for use in a proposed cementing operationinvolving forming a wellbore load resistant cement sheath within anannulus between the subterranean salt formation and casing, and whereinthe wellbore load resistant cement sheath is resistant to wellboreloads; (d) experimentally determining whether the proposed cement slurryis capable of forming the wellbore load resistant cement sheath at thefirst location based on actual thermal and thermo-mechanical propertiesof the proposed cement slurry; (e) theoretically determining whether theproposed cement slurry is capable of forming the wellbore load resistantcement sheath at the first location, the theoretical determinationcomprising: (e)(1) designing an electronic, cross-section geometricmodel of the subterranean salt formation at the first location, whereinthe geometric model represents the subterranean salt formation, thecasing, and the proposed cement slurry after curing, and (e)(2)simulating a plane-strain condition of the wellbore loads on the curedproposed cement slurry at the first location in the subterraneanformation using the geometric model, (f) establishing a final cementslurry capable of forming the wellbore load resistant cement sheath; and(g) performing a final cementing operation with the final cement slurryin the subterranean salt formation.
 2. The method of claim 1, whereinthe salt creep profile in step (b) is experimentally determined by amethod selected from the group consisting of: (b1) obtaining at leastone wellbore core sample of the wellbore in the subterranean formationat the first location, and performing a core sample salt creep loadmeasurement using the wellbore core sample, (b2) performing a downholesalt creep load measurement at the first location in the wellbore in thesubterranean formation, (b3) obtaining an offset well salt creep loadmeasurement and performing a parametric analysis thereon, wherein theoffset well and the wellbore in the subterranean salt formation arelocated in a same oil field, and any combination thereof.
 3. The methodof claim 1, wherein whether the proposed cement slurry is capable offorming the wellbore load resistant cement sheath in step (d) isexperimentally determined by a method selected from the group consistingof: (d1) curing the proposed cement slurry, and performing an ultrasoniccement analyzer test on the cured proposed cement slurry, (d2) curingthe proposed cement slurry, and performing uniaxial and triaxialcompression tests on the cured proposed cement slurry, and anycombination thereof.
 4. The method of claim 1, wherein the plane-straincondition of the wellbore loads on the cured proposed cement slurry atthe first location in the subterranean formation using the geometricmodel in step (e)(2) is simulated based the wellbore loads and one orboth of: theoretical thermal and thermo-mechanical properties of thecured proposed cement slurry, or the actual thermal andthermo-mechanical properties of the cured proposed cement slurry in step(d).
 5. The method of claim 4, wherein step (e) is performed before step(d), wherein step (e)(2) is simulated based on the theoretical thermaland thermo-mechanical properties, and further comprising repeating asecond step (e) after step (d) wherein the second step (e) comprisesstep (e)(2) of simulation based on the actual theoretical thermal andthermo-mechanical properties in step (d).
 6. The method of claim 1,further comprising either performing step (d) before step (e), orperforming step (e) before step (d).
 7. The method of claim 1, furthercomprising manipulating the proposed cement slurry after step (d), andrepeating steps (d) through (e) until the proposed cement slurry iscapable of forming the wellbore load resistant cement sheath.
 8. Themethod of claim 1, further comprising manipulating the proposed cementslurry after step (e), and repeating steps (d) through (e) until theproposed cement slurry is capable of forming the wellbore load resistantcement sheath.
 9. The method of claim 1, further comprising a tubularextending into the wellbore in the subterranean salt formation, and apump fluidly coupled to the tubular; and wherein step (g) is performedby introducing the final cement slurry into the wellbore through thetubular.
 10. A method comprising: (a) providing a wellbore in asubterranean salt formation, wherein the subterranean salt formationcomprises intercalated salts along a first length of the wellbore; (b)experimentally determining a salt creep profile for the intercalatedsalts at the first length of the wellbore in the subterranean formation;(c) designing a proposed cement slurry based on the salt creep profile,the proposed cement slurry having a rheology profile, wherein theproposed cement slurry is designed for use in a proposed cementingoperation involving forming a wellbore load resistant cement sheathwithin an annulus between the subterranean salt formation and casing,and wherein the wellbore load resistant cement sheath is resistant towellbore loads; (d) experimentally determining whether the proposedcement slurry is capable of forming the wellbore load resistant cementsheath at the first length based on actual thermal and thermo-mechanicalproperties of the proposed cement slurry; (e) theoretically determiningwhether the proposed cement slurry is capable of forming the wellboreload resistant cement sheath at the first length, the theoreticaldetermination comprising: (e)(1) designing an electronic, longitudinalgeometric model of the subterranean salt formation at the first length,wherein the geometric model represents the subterranean salt formation,the casing, and the proposed cement slurry after curing, and (e)(2)simulating an axisymmetric condition or a three-dimensional condition ofthe wellbore loads on the cured proposed cement slurry at the firstlocation in the subterranean formation using the geometric model, (f)establishing a final cement slurry capable of forming the wellbore loadresistant cement sheath; and (g) performing a final cementing operationwith the final cement slurry in the subterranean salt formation.
 11. Themethod of claim 10, wherein the salt creep profile in step (b) isexperimentally determined by a method selected from the group consistingof: (b1) obtaining at least one wellbore core sample of the wellbore inthe subterranean formation at the first length, and performing a coresample salt creep load measurement using the wellbore core sample, (b2)performing a downhole salt creep load measurement at the first length inthe wellbore in the subterranean formation, (b3) obtaining an offsetwell salt creep load measurement and performing a parametric analysisthereon, wherein the offset well and the wellbore in the subterraneansalt formation are located in a same oil field, and any combinationthereof.
 12. The method of claim 10, wherein whether the proposed cementslurry is capable of forming the wellbore load resistant cement sheathin step (d) is experimentally determined by a method selected from thegroup consisting of: (d1) curing the proposed cement slurry, andperforming an ultrasonic cement analyzer test on the cured proposedcement slurry, (d2) curing the proposed cement slurry, and performinguniaxial and triaxial compression tests on the cured proposed cementslurry, and any combination thereof.
 13. The method of claim 10, whereinthe axisymmetric condition or the three-dimensional condition of thewellbore loads on the cured proposed cement slurry at the first lengthin the subterranean formation using the geometric model in step (e)(2)is simulated based the wellbore loads and one or both of: theoreticalthermal and thermo-mechanical properties of the cured proposed cementslurry, or the actual thermal and thermo-mechanical properties of thecured proposed cement slurry in step (d).
 14. The method of claim 13,wherein step (e) is performed before step (d), wherein step (e)(2) issimulated based on the theoretical thermal and thermo-mechanicalproperties, and further comprising repeating a second step (e) afterstep (d) wherein the second step (e) comprises step (e)(2) of simulationbased on the actual theoretical thermal and thermo-mechanical propertiesin step (d).
 15. The method of claim 10, wherein the electronic,longitudinal geometric model is a three-dimensional model.
 16. Themethod of claim 10, further comprising either performing step (d) beforestep (e), or performing step (e) before step (d).
 17. The method ofclaim 10, further comprising manipulating the proposed cement slurryafter step (d), and repeating steps (d) through (e) until the proposedcement slurry is capable of forming the wellbore load resistant cementsheath.
 18. The method of claim 10, further comprising manipulating theproposed cement slurry after step (e), and repeating steps (d) through(e) until the proposed cement slurry is capable of forming the wellboreload resistant cement sheath.
 19. The method of claim 10, furthercomprising repeating steps (b) through (e) at at least a second lengthof the wellbore in subterranean salt formation, wherein the electronic,longitudinal geometric model designed in step (e)(1) represents thefirst length and at least the second length.
 20. The method of claim 10,further comprising a tubular extending into the wellbore in thesubterranean salt formation, and a pump fluidly coupled to the tubular;and wherein step (g) is performed by introducing the final cement slurryinto the wellbore through the tubular.